Field of the Invention
The invention of the instant application relates to a gear stage assembly with two meshing gearwheels for mechanically transmitting a torque, individual magnets being arranged on each gearwheel in a ringlike manner corresponding to the gearwheel teeth, for producing magnetic forces in the gear stage.
A gear stage assembly of this type has become known heretofore from the published German Patent Document DE 195 44 099 A1, at least one of the mutually associated gearwheels of a respective gear stage being magnetized and the gearwheels being attracted to one another by magnetic force. For this purpose, a permanently magnetic or a permanently magnetized material is provided in a layer fixedly resting on a front face of the magnetized gearwheel. In this regard, the layer has an axial polarization of uniform alignment over the circumference, so that one pole, respectively, faces towards the gearwheel, and the other pole faces away from it. Furthermore, a cross section of the layer perpendicular to the axis of rotation has an outline or outer contour which is at a slight distance from the circumferential edge of the gearwheel. In accordance with the state of the prior art, provision is thus made for the mutually associated load-free gearwheels, e.g., the tooth faces or flanks of a fixed and of a loose wheel, to be attracted by magnetic force. The tooth faces thus always rest against one another, regardless of whether power is being transmitted, i.e. in the engaged condition, or not, i.e., in the disengaged condition. A disadvantage of the prior art construction is, in particular, that alternating face or flank contact cannot be avoided when there is an imbalance in gearwheels or gear stages of relatively large mass.
Furthermore, varnishing units are generally known in the printing-machine industry and, therein, alternating tooth face contact can occur, for example, between the varnishing-blanket cylinder and the impression cylinder. Alternating tooth face contact is often caused by the unbalanced varnishing-blanket cylinder. This imbalance can typically be as much as about 6 Nm, for example. Due to the alternating tooth face contact, at one printing speed, the print start varies randomly from sheet to sheet, within the range of the tooth backlash, and also varies from printing speed to printing speed. This leads to registration problems and hence to lower print quality. To eliminate alternating tooth face contact, it is necessary to compensate for the maximum imbalance moment of the cylinder.
The two effects described can be avoided by installing a motorized brake with a braking torque of, for example, 10 Nm. A disadvantage, in this regard, however, is that a motor driving the gear system has to produce this torque additionally.
The publication entitled xe2x80x9cSonderdruck aus xe2x80x98Der Konstrukteurxe2x80x99xe2x80x9d (Reprint from xe2x80x9cThe Designerxe2x80x9d] 7-8/93; pp 28, 29 describes a permanent-magnetic gear made by the firm Gerwah-Prxc3xa4zision, Gesellschaft fxc3xcr Servokomponenten und Messtechnik mbH D-63868 Groxcex2wallstatt, Germany. In the case of a magnetic spur gear, the two magnet wheels form two magnet rings that are magnetized with a plurality of poles radially or laterally on the circumference and are firmly connected to the output shaft of the gear and to the motor shaft. Constantly magnetized permanent magnet rings are used as the magnetic material (e.g., rare-earth magnets or ferrite magnets). Although both magnet rings have different diameters and numbers of poles, they have the same height to ensure optimum torque transmission for the minimum possible use of permanent magnet material. The magnet rings are arranged so that pole surfaces of opposite polarity lie opposite one another in the narrowest air gap. If the magnet wheel that is firmly connected to the motor shaft is moved in either direction of rotation, the magnet wheel that is firmly connected to the output shaft follows suit in the opposite direction of rotation in accordance with the transmission ratio, due to the direct magnetic coupling of this rotary motion. The maximum torque that can be transmitted occurs when the magnet poles are rotated over half of the position of the poles relative to the other magnet wheel. Overloading of the gear does not lead to destruction of the wheels. On the contrary, the magnetic gear simultaneously performs the function of a slipping clutch.
It is accordingly an object of the invention to provide a gear stage with a preload torque of the type mentioned in the introduction hereto, wherein alternating tooth face contact is avoided.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a gear stage assembly having a gear stage with two meshing gearwheels for mechanically transmitting a torque, comprising individual magnets arranged in the form of a ring on each of the gearwheels in a manner corresponding to that of the teeth of the gearwheels, for producing magnetic forces in the gear stage, individual magnets of respective ones of the magnets formed in a ring being arranged with alternating polarity in the direction of rotation and forming a stage of magnets in a ring disposed parallel to the gear stage, for producing a preload torque in the gear stage.
In accordance with another feature of the invention, the two gearwheels are mounted so as to be movable axially relative to one another.
In accordance with a further feature of the invention, the magnets are permanent magnets, and the permanent magnets of one of the gearwheels are formed wider in the axial direction than the permanent magnets of the other of the gearwheels of the gear stage, and wherein the two gearwheels are mounted so as to be movable axially relative to one another.
In accordance with an added feature of the invention, the individual magnets, respectively, are provided on a magnet wheel which is connected to a respective gearwheel so as to be fixed against rotation relative thereto.
In accordance with an additional feature of the invention, the individual magnets are distributed equidistantly with a pitch over the circumference of the gearwheels.
In accordance with yet another feature of the invention, the individual magnets of the two magnet wheels are arranged in positions displaced a given value from one another.
In accordance with yet a further feature of the invention, the given value is half the magnet pitch.
In accordance with yet an added feature of the invention, the gearwheels have a helical toothing, and axial travel of the gearwheels is limited to a maximum value.
In accordance with a concomitant aspect of the invention, there is provided a varnishing unit with a gear stage assembly having a gear stage with two meshing gearwheels for mechanically transmitting a torque, comprising individual magnets arranged in the form of a ring on each of the gearwheels in a manner corresponding to that of the teeth of the gearwheels, for producing magnetic forces in the gear stage, individual magnets of respective ones of the magnets formed in a ring being arranged with alternating polarity in the direction of rotation and forming a stage of magnets in a ring disposed parallel to the gear stage, for producing a preload torque in the gear stage.
According to the invention, the aforementioned objects are achieved by providing a gear stage assembly with individual magnets of a magnet wheel, which are arranged with alternating polarity in the direction of rotation and form a magnet-wheel stage, parallel to the gear stage, for the production of a preload torque in the gear stage. The system thereby obtained is contact-free, wear-free and inexpensive and provides high preload torques while being of simple design and narrow width in construction. In particular, an autonomous system that requires no additional energy is also achieved thereby.
According to a preferred embodiment, the permanent magnets of one gearwheel are made wider in the axial direction than the permanent magnets of the other gearwheel of the gear stage, and the two gearwheels and magnet wheels are mounted so that they can be moved axially relative to one another. This ensures that a constant and defined preload torque acts in every axial position of the two gearwheels or magnet wheels. According to the invention, there are furthermore no axial forces acting during the process of movement. Because one magnet wheel is made wider than the other magnet wheel by an amount corresponding to the amount of travel, the other magnet wheel remains invariably in the magnetic field at all times during the movement, and the set preload torque thus remains constant.
As an alternative or as an addition, it is also possible to change the degree of overlap of the magnet elements in a simple manner by the axial movement of the two gearwheels or magnet wheels, especially if both magnet wheels are of the same width. As a result, the magnitude of the preload torque in the gear stage can be adjusted without problems as a function of the operating conditions, and the gear stage can be operated with a definite preload torque.
The individual magnets are each advantageously arranged on a magnet wheel that is connected in a rotationally fixed manner to the gearwheel or the shaft of the gear stage. This provides a construction that is simple in terms of design, and can be retrofitted or replaced quickly.
To produce a preload torque that acts as uniformly as possible, the individual magnets are distributed equidistantly over the circumference of the gearwheels and magnet wheels, respectively. The individual magnets of the two magnet stages are advantageously arranged in positions displaced by half the magnet pitch relative to one another. A maximum preload torque in the gear stage can thereby be achieved for a given size of the magnet elements and given positioning of the magnet wheels relative to one another.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a gear stage assembly with a preload torque, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: